I've taught students to go to advanced search and then click on MORE - and enter the web page that they are evaluating into the "Find pages that link TO this page" as one of the criteria of evaluating a web pages credibility.

It doesn't appear to be there anymore. This is one of the 21st century skills used to evaluate web pages.

I know that I can enter "link:mywebpage" into the google search bar. But I was trying to teach students that they didn't need to memorize it.

The link command has not been accurate in years, so it makes sense for Google to remove it. It does work as link:www.domain.com but again, it is not accurate. Removing it from the advanced search page does make sense, if it isn't accurate.